Microsoft added the Model-View-Controller based framework to ASP.NET.
This allows developers to build Web applications as a composite of three different roles, namely the Model, View and Controller.
The Model represents the state of the application, usually stored in a database table.
The View extracts information from the model and displays the information.
Finally, the Controller updates the model to reflect the change in state of the application.

ASP.NET Identity - The MVC project templates are updated to use ASP.NET Identity for authentication and identity management which supports third party login providers like Facebook, Twitter, Google, etc….

Filter Overrides - It is now possible to override filters on a method or controller by specifying an override filter.

Attribute Routing - The Attribute routing nuget package is now integrated into MVC 5 and allows you to specify routes by annotating actions and controllers.

With ASP.NET MVC 4 Hosting

ASP.NET Web API - ASP.NET Web API is a framework that helps ease building HTTP services to reach users through browsers and mobile devices. ASP.NET Web API is a platform for building RESTful applications on the .NET Framework.

Refreshed default project templates - The product templates are revamped with a more modern feel.

Mobile application development support - This includes new mobile project template to make it easier to build applicaitons for mobile and tablet browsers. The template is based on jQuery Mobile for touch-optimized UI.

Enhanced support for asynchronous methods - You can now code asynchronous action methods as single methods that return an object of type Task or Task &ltActionResult&gt.

Bundling and Minification - This framework helps you reduce the amount of HTTP requests that a Web page makes by combining individual files into a single, bundled file for scripts and CSS. The overall request size is further reduced by minifying the contents of the bundle. Minifying includes activities like eliminating whitespace or shortening variable names or collapsing CSS selectors based on their semantics.

and more...

With ASP.NET MVC 3 Hosting

Razor - MVC 3 ships with a new view-engine option called Razor which minimizes the number of characters and keystrokes required when writing a view template, and improves coding workflow.